This invention relates to improved orthodontic screw-type biassing devices, and more particularly to improvements which prevent backing off of the screw which imparts the biassing force.
Prior orthodontic biassing devices of the type to which the present invention pertains generally comprise first and second body members interconnected by a screw member having oppositely threaded ends. As the screw member is rotated, the body members are spread further and further apart, thereby imparting orthodontic biassing forces in the mouth of a patient. The reaction forces against the body members are large, and in some instances are sufficiently high to cause the screw to back off (i.e. rotate in a reverse direction under the influence of the reaction forces applied to the body members), thereby reducing the applied biassing force. The undesirable phenomenon of the screw backing off under the influence of reaction forces applied to the body members is denoted herein as "screw back-off".
The object of the present invention is to provide improved orthodontic biassing devices, of the type discussed above, which substantially prevent or substantially reduce the screw back-off inherent in existing devices.